drm/xe/ufence: Prefetch ufence addr to catch bogus address

drm/xe/ufence: Prefetch ufence addr to catch bogus address

access_ok() only checks for addr overflow so also try to read the addr
to catch invalid addr sent from userspace.

Link: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/1630
Cc: Francois Dugast <francois.dugast@intel.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Matthew Auld <matthew.auld@intel.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241016082304.66009-2-nirmoy.das@intel.com
Signed-off-by: Nirmoy Das <nirmoy.das@intel.com>